In general CMP involves the concurrent chemical and mechanical polishing of an overlying first layer to expose the surface of a non-planar second layer on which the first layer is formed. Briefly, a CMP process generally uses a polymeric polishing pad and a slurry that includes chemicals and abrasive particles to remove a first layer at a faster rate than a second layer until the surface of the overlying first layer of material becomes coplanar with the upper surface of the covered second layer. The abrasive particles are typically oxides of silicon, aluminum, zirconium or carbides or nitrides of silicon. The slurry chemicals typically include surfactants, oxidants and pH control additives. For planarization of a three layer film stack, due to selectivity considerations, at least two different CMP processes are generally used in conjunction with a separate chemical etch process. Typically, the two different CMP processes are carried out on separated platens, and even separate CMP systems because different chemistries, and therefore different slurry compositions, are needed to polish each layer. For example, in the case of a two layer silicon oxide/silicon nitride film stack, for removing excess silicon oxide, the CMP chemistry typically has a low oxide/nitride selectivity, while the chemistry used for controlled removal of a portion of the nitride has a reduced rate of nitride removal. As compared to a hypothetical single step process, such multi-step processing adds to cycle time, adds to fabrication cost, and can increase defect density. What is needed is a CMP processes that can reduce the number steps involved in CMP processing of a three or more layer film stack.